1. Field of the Invention
The invention relates to a high power density sorption heat store, in particular for the temporal-periodical storage of available heat, and to a method of heat storage.
2. Description of Related Art
Sorption heat stores are used to temporally and locally store periodically recurring heat energies with the help of a working fluid, in a targeted and user-friendly way allowing the power to be unloaded again, in a sorption-active micro-porous solid matter storage material. Preferred applications concern the seasonal or short-term storage of heat in housing and building technologies for heating and air-conditioning of rooms or to heat service water. Modern systems of sorption storage consist, as a rule, of a heat-insulated container that is periodically loaded with heat power in a targeted manner, and is again unloaded upon recall. For this purpose, the working fluid is periodically transformed in a gaseous state by means of vaporizers, and is bound to suitable porous sorbents during the storage unloading process. During this, sorption heat is released, which can be supplied to further liquid or gaseous heat exchangers via circuits for the available heat. In the loading process of the stores, a removal of the working fluid from sorbents is carried out through means of desorption. This ensues by feeding heat from power supply networks or, preferably, from other locally available sources of heat, such as devices for obtaining solar power or geothermal heat, with the working fluid being again liquefied in associated condensers. Less expensive thermal or electric forms of power may thus be stored during slack periods in power supply networks, with the advantage of then having additional amounts of available heat to be drawn on in periods of increased power demand.
According to xe2x80x9cSorptionsspeicherxe2x80x94Saisonale Wxc3xa4rmespeicherung mit hohen Energiedichtenxe2x80x9d (Sorption storesxe2x80x94seasonal heat storage with high power densities), a company publication of UFE SOLAR GmbH, Alfred-Nobel-Strasse 1, D-16225 Eberswalde/Brandenburg, written by W. Mittelbach and H.-M. Henning, the power densities exceed those of a conventional water storage unit by four to five times, depending on the depth and range of the storage state created.
In more recent proposals concerning sorption stores, it is asserted to increase the power storage densities and the thermal efficiency initially by introducing verbal concepts such as xe2x80x9ccompact storexe2x80x9d or xe2x80x9chigh-performance storexe2x80x9d and the technical measures derived therefrom, in that, on the whole, in a space delimited due to the geometric dimensions of the apparatus, the at least three, originally spatially separated areas sorption area, vaporizer and/or condensation area, and an area for stocking the working fluid, normally water, are united in one common container. Solutions like this (cf. DE 40 19 669, DE 198 11 302, and EP 0 897 094) are relatively simple to manufacture and can be installed in secondary rooms of buildings, e.g., of houses, and may be operated with a certain expenditure for the regulation and control alone of valves, serving the purpose of heating, air-conditioning and preparing service water.
As a rule, the vaporizer and condenser are arranged below the sorbent chamber, and are periodically successively flowed through in most cases by two circuits representing alternatingly switched heat exchange circuits of fossil fuel-operated heating means and solar or geothermal circuits. The sorption-active store volume must be capable of being evacuated and hermetically sealed, in order to make maximum use of the cyclically reversible loading cycle existing between the loading and unloading process. Hence, the task of any development of a sorption store is to maximize this loading cycle that is determined pressure-dependent by two separated isotherms involved in the adsorption and desorption process.
In this process, however, basic problems arise in conjunction with the transport processes for fluid and heat with regard to the heating, cooling and working fluids both in the inner container volume, as well as via the surfaces of the conduit systems providing for said transport:
The sorbents exhibit a markedly restricted heat conductivity, so that the desired positive heat balance is impeded in a preferred direction of the container, but also in one of its transverse directions. As a rule, the sorbents consist of granulized or pelletized particles, which, in the form of grain beds, are present between the heat and flow conducting equipment. For increasing the storage density, high filling portions are sought, whereby necessary installations imparting the heat restrict the storage-active space.
The free paths for the transport of the working fluid are reduced within the beds due to the desired higher filling proportions with sorbents. Moreover, the sorbents have outer and inner pore systems, which have to be filled with working fluid as completely as possible, so as to achieve a high storage density.
By combining vaporizer and condenser parts within one receptacle and in a narrow space, xe2x80x9cbridgesxe2x80x9d short-circuiting the transport processes arise across the heat and flow conducting equipment within the receptacle, which shorten the desired course of the balance processes throughout the entire sorbent space and contribute to a flow bypass formation reducing the efficiency.
In a configuration of the sorption store in a compactness which is not optimally high, the proportion of the external heat insulation has to be relatively large, so as to achieve that a sufficient power density remains maintained over a longer period of time. Internal insulations between the vaporizer and condenser, however, would additionally reduce the storage density. Accordingly, with an increase of the dimensional scale, the proportion of the external insulation may be reduced in that a temperature gradient is established from the inner and warmer to the outer and cooler spaces.
The more recent approaches scarcely furnish indications as to how to solve these problems, either.
It is, however, known that usual modern heat exchangers, e.g. designed as tube bundle or jacketed heat exchangers, are able to limit and even reduce these problems to a high degree with an optimal formation and configuration of up to several meters in diameter. Heat exchangers are available in standardized constructions and series established, for example, by norms for tubular bundle heat exchangers, such as the German Standards DIN 28 182: Rohrleitungen, Durchmesser der Bohrungen in Rohrbxc3x6den, Umlenksegmenten und Stxc3xctzplatten; DIN 28 185: Rohrbxc3xcndel-Einbauten or DIN 28 008: Abmaxcex2e und Toleranzen. The correspondingly highly sophisticated knowledge on their design and dimensions is likewise contained in standard works, such as in the handbooks xe2x80x9cVerfahrenstechnische Berechnungsmethodenxe2x80x9d Teil 1xe2x80x94Wxc3xa4rmexc3xcbertrager; Teil 5xe2x80x94Chemische Reaktoren; Apparate, Ausrxc3xcstung und ihre Berechnung, published by Deutscher Verlag fxc3xcr Grundstoffindustrie, Leipzig, 1981.
Furthermore, it is known from DE 39 25 704 that using ribbed tubes as inner tubes, a relatively long travel path and a large transfer surface for the second heat transfer medium around the inner tube, and hence a good heat transmission is achieved in that, for example, a flexible hose structure forming a flow channel is shrunk onto the ribs. Such modified ribbed tubes, however, do not yet allow a suitable guidance of the flow of working medium which must be in connection with the sorbent via openings. For this reason, more recent arrangements as in DE 195 39 105 relate to so-called sorption heat exchangers, in which the channels for the working fluid flowing in vapor form and the inner heat-conducting elements are largely matched to one another in one of the transverse dimensions. So as to increase the dimensional scale, a favorable guidance of the working fluid may also ensue in a preferred longitudinal direction (the main axis of the apparatus), which guidance, however, is not yet assured with the chosen known arrangement of heat-conducting lamellae. In sorption heat stores, the possibilities of increasing the dimensional scale are limited by the fact that, process-contingently, the solid sorbent cannot be moved like a fluid.
The concern of realizing the vaporization and condensation processes in one common apparatus and in a compact configuration, to date has only been introduced on a major economic scale in the field of thermal material separation, such as distillation and rectification, e.g. for separating hydrocarbon mixtures to obtain fuel for internal combustion engines. In water vaporization and condensation processes, e.g. for the purpose of water purification, this process may then turn out to be uneconomic, due to the high vaporization heats required, when a combined heat process between various partial processes or apparatus parts is not given, e.g. by means of heat pumps. The efficiency of vaporization and condensation processes, such as e.g. in DE 196 46 458 and DE 196 47 378 concerning the field of water treatment and water purification, may be increased in that vaporizer and condenser are neighboring each other, that a stepped heat gradient exists between these two, and that the condensation of the vapor ensues in a direct heat contact by means of a guidance through the condensate which is already present, at least proportionately. This heat pump effect in a way simulated is advantageously achieved within contact condensers and by slowing down the two-phase mixture flowing through the condenser while condensing. In a variant of the sorption heat store as per DE 198 11 302, a so-called tank-in-tank arrangement, it is already indicated that the active storage volume is enclosed by a condenser or by the condensate container. With respect to a decreasingly graduated heat transfer from the inside to the outside, this arrangement has advantages in the transverse dimensions, in that in the interior of the store, a heated storage volume forms having a temperature gradient in the peripheral direction, a condensation zone arises having a low temperature, so that the outer heat insulation of the container is to a certain extent relieved in its heat-insulating functions, and correspondingly may be designed lower. In a schematic representation of the condensation device, however, here, as well, statements as to their configuration are not made. No other solutions became known either, in which the vaporization of the working fluid takes place directly in the store and in the immediate proximity of the sorbent chamber.
The invention relates to a high power density sorption heat store, preferably for storing low-temperature heats, and is characterized in that, in accordance with the state of the art, simple instrumental extensions for the heat conduction and flow guidance of the working fluid are incorporated in commercially available and standardized heat exchangers of various types for fluid and heat transformation in solid matters, which instrumental extensions achieve an improvement of the thermal efficiency due to a combined heat process in the sorption heat store 1 itself, a tube jacket 2 being provided having tube bottoms 3, 3xe2x80x2 and heat exchange tubes 4 penetrating the sorption layer between the carrier floors 6, 6xe2x80x2, with mat layers 9, 9xe2x80x2 being in each case located in between, the tube jacket 2 being essentially enclosed by a working fluid tank 10 comprising working fluid lines 11, 11xe2x80x2 including the valves 12, 12xe2x80x2, which in turn are in communication with the mat layers 9, 9xe2x80x2, and the dip tank 13 comprising the passage 16 in the bottom area, as well as that heat exchange tubes 4 are proportionately provided with ribs 27 and are loosely guided through openings 29 of the carrier floor 6xe2x80x2 and the mat layer 9xe2x80x2, but are fixedly connected with the tube bottoms 3, 3xe2x80x2, and the ribs 27 are enclosed by a finely perforated network 28. The associated method relates to the autothermal vaporization of the working fluid, whereby in a unloading process in a first step the liquid level in the working fluid tank 10 goes over by flowing from the stand-by condition (a) into the start condition (b), and in a second step, a vaporization of the remaining liquid content of the working fluid tank 10 takes place.